135 research outputs found
Performance evaluation of synergic operation of algorithms enabling opportunistic networks - D4.3
Deliverable D4.3 del projecte OneFITPreprin
Mobile Ad-Hoc Networks
Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: vehicular ad-hoc networks, security and caching, TCP in ad-hoc networks and emerging applications. It is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks
Alocação de recursos para sistemas móveis multi-utilizador e multi-antena
Doutoramento em Engenharia ElectrotécnicaThe thesis addresses the sum rate or spectral e ciency maximization problem
in cellular systems with two main components, multiple antennas and
multiple users. In order to solve such a problem, several resource allocation
techniques are studied and developed for di erent cellular scenarios. The
antennas at the transmitters are arranged in several con gurations, i.e.,
co-located or distributed and for such arrangements di erent levels of coordination
and cooperation between transmitters are investigated. Accounting
for more receiver antennas than transmitter antennas implies that system
optimization must select the best transmitter-receiver match (combinatorial
problem) which can be solved with di erent degrees of cooperation between
transmitters. The system models studied can be classi ed either as interference
limited or as power limited systems.
In interference limited systems the resource allocation is carried out independently
by each transmitter which yield power leakage to unintended
receivers. For this kind of systems, the access network using distributed
antenna architectures is examined. The properties of distributed antenna
in cellular systems as well as the gains they provide in terms of frequency
reuse and throughput are assessed. Accounting for multiple user scenarios,
several techniques and algorithms for transmitter-receiver assignment,
power allocation, and rate allocation are developed in order to maximize
the spectral e ciency.
In power limited systems the transmitters jointly allocate resources among
transmit and receive antennas. The transmitters are equipped with multiple
antennas and signal processing is implemented in order to suppress inter-user
interference. Single-cell and multi-cell systems are studied and the problem
of sum rate maximization is tackled by decoupling the user selection and
the resource allocation (power and precoding) processes. The user selection
is a function of the type of precoding technique that is implemented
and the level of information that can be processed at the transmitter. The
developed user selection algorithms exploit information provided by novel
channel metrics which establish the spatial compatibility between users.
Each metric provides a di erent trade-o between the accuracy to identify
compatible users, and the complexity required to compute it. Numerical
simulations are used to assess the performance of the proposed user selection
techniques (metrics and algorithms) whose performance are compared
to state-of-the-art techniques.Esta tese descreve o problema da maximização da taxa de transmissão ou
e ciência espectral em sistemas moveis tomando em atenção duas características fundamentais destes, o número de antenas e utilizadores.
A fim de resolver este tipo de problema, várias técnicas de alocação de recursos
foram estudadas e propostas para diferentes cenários. As antenas nos transmissores
estão organizadas em diferentes configurações, podendo ser localizadas
ou distribuídas e para estes esquemas, diferentes níveis de cooperação
e coordenação entre transmissores foram investigados. Assumindo mais antenas
receptoras do que antenas transmissoras, implica que a otimização do
sistema seleccione as melhores combinações de transmissor-receptor (problema
combinatório), o que pode ser concretizado usando diferentes graus
de cooperação entre transmissores. Os modelos de sistemas estudados, podem
ser classificados como sistemas limitados por interferência ou sistemas
limitados por potência.
Em sistemas limitados por interferência a alocação de recursos e feita independentemente
para cada transmissor o que resulta em perda de energia
para os receptores não tomados em consideração. Para este tipo de sistemas,
e considerado o caso em que a rede de acesso e constituída por antenas
distribuídas. Os ganhos obtidos devido ao uso de antenas distribuídas,
quer em termos do planeamento de frequências quer da maximização da taxa
de transmissão são considerados. Assumindo esquemas multi-utilizador,
várias técnicas e algoritmos de transmissão-recepção, alocação de potência
e de taxa de transmissão foram desenvolvidos para maximizar a e ciência
espectral.
Para sistemas limitados em potência os transmissores alocam os recursos
quer de antenas de transmissão quer de recepção conjuntamente. Os transmissores
estão equipados com várias antenas e o processamento de sinal e
implementado de modo a eliminar a interferência entre utilizadores. Sistemas
de célula única e de múltiplas células foram estudados. Para estes foi
considerado o problema da maximização de taxa de transmissão o qual foi
resolvido heuristicamente, através do desacoplamento do problema em duas
partes, uma onde se efectua a seleção de utilizadores e outra onde se considera
a alocação de recursos. A seleção de utilizadores e feita em função do
tipo de técnicas de pré-codificação implementadas e do nível de informação
que o transmissor possui. Os algoritmos de seleção de utilizadores desenvolvidos
verificam a compatibilidade espacial entre utilizadores, usando para
tal métricas propostas. Cada uma das métricas oferece um trade-off diferente
entre a precisão para identificar um utilizador compatível e a complexidade
necessária para a implementar. Foram usadas simulações numéricas
para avaliar a performance das técnicas de seleção de utilizadores propostas
(métricas e algoritmos), performance que foi comparada com as técnicas
mais inovadoras
Formulation, implementation considerations, and first performance evaluation of algorithmic solutions - D4.1
Deliverable D4.1 del projecte Europeu OneFIT (ICT-2009-257385)This deliverable contains a first version of the algorithmic solutions for enabling opportunistic networks. The presented algorithms cover the full range of identified management tasks: suitability, creation, QoS control, reconfiguration and forced terminations. Preliminary evaluations complement the proposed algorithms. Implementation considerations towards the practicality of the considered algorithms are also included.Preprin
Interference Management in Dense 802.11 Networks
Wireless networks are growing at a phenomenal rate. This growth is causing an overcrowding of the unlicensed RF spectrum, leading to increased interference between co-located devices. Existing decentralized medium access control (MAC) protocols (e.g.
IEEE 802.11a/b/g standards) are poorly designed to handle interference in such dense
wireless environments. This is resulting in networks with poor and unpredictable performance, especially for delay-sensitive applications such as voice and video.
This dissertation presents a practical conflict-graph (CG) based approach to designing self-organizing enterprise wireless networks (or WLANs) where interference is centrally managed by the network infrastructure. The key idea is to use potential interference information (available in the CG) as an input to algorithms that optimize the parameters
of the WLAN.We demonstrate this idea in three ways. First, we design a self-organizing
enterprise WLAN and show how the system enhances performance over non-CG based
schemes, in a high fidelity network simulator. Second, we build a practical system for conflict graph measurement that can precisely measure interference (for a given network configuration) in dense wireless environments. Finally, we demonstrate the practical benefits
of the conflict graph system by using it in an optimization framework that manages
associations and traffic for mobile VoIP clients in the enterprise.
There are a number of contributions of this dissertation. First, we show the practical
application of conflict graphs for infrastructure-based interference management in dense wireless networks. A prototype design exhibits throughput gains of up to 50% over traditional approaches. Second, we develop novel schemes for designing a conflict graph measurement system for enterprise WLANs that can detect interference at microsecond-level
timescales and with little network overhead. This allows us to compute the conflict
graph up to 400 times faster as compared to the current best practice proposed in the
literature. The system does not require any modifications to clients or any specialized
hardware for its operation. Although the system is designed for enterprise WLANs, the
proposed techniques and corresponding results are applicable to other wireless systems as well (e.g. wireless mesh networks). Third, our work opens up the space for designing novel fine-grained interference-aware protocols/algorithms that exploit the ability to compute the conflict graph at small timescales. We demonstrate an instance of such a system with the design and implementation of an architecture that dynamically manages client associations and traffic in an enterprise WLAN. We show how mobile clients sustain uninterrupted and consistent VoIP call quality in the presence of background interference for the duration of their VoIP sessions
Practical interference management strategies in Gaussian networks
Increasing demand for bandwidth intensive activities on high-penetration wireless hand-held
personal devices, combined with their processing power and advanced radio features, has
necessitated a new look at the problems of resource provisioning and distributed management
of coexistence in wireless networks. Information theory, as the science of studying
the ultimate limits of communication e ciency, plays an important role in outlining guiding
principles in the design and analysis of such communication schemes. Network information
theory, the branch of information theory that investigates problems of multiuser and
distributed nature in information transmission is ideally poised to answer questions about
the design and analysis of multiuser communication systems. In the past few years, there
have been major advances in network information theory, in particular in the generalized
degrees of freedom framework for asymptotic analysis and interference alignment which have
led to constant gap to capacity results for Gaussian interference channels. Unfortunately,
practical adoption of these results has been slowed by their reliance on unrealistic assumptions
like perfect channel state information at the transmitter and intricate constructions
based on alignment over transcendental dimensions of real numbers. It is therefore necessary
to devise transmission methods and coexistence schemes that fall under the umbrella of
existing interference management and cognitive radio toolbox and deliver close to optimal
performance.
In this thesis we work on the theme of designing and characterizing the performance of
conceptually simple transmission schemes that are robust and achieve performance that is
close to optimal. In particular, our work is broadly divided into two parts. In the rst part,
looking at cognitive radio networks, we seek to relax the assumption of non-causal knowledge
of primary user's message at the secondary user's transmitter. We study a cognitive channel
model based on Gaussian interference channel that does not assume anything about users
other than primary user's priority over secondary user in reaching its desired quality of
service. We characterize this quality of service requirement as a minimum rate that the
primary user should be able to achieve. Studying the achievable performance of simple
encoding and decoding schemes in this scenario, we propose a few di erent simple encoding
schemes and explore di erent decoder designs. We show that surprisingly, all these schemes
achieve the same rate region. Next, we study the problem of rate maximization faced by
the secondary user subject to primary's QoS constraint. We show that this problem is not
convex or smooth in general. We then use the symmetry properties of the problem to reduce
its solution to a feasibly implementable line search. We also provide numerical results to
demonstrate the performance of the scheme.
Continuing on the theme of simple yet well-performing schemes for wireless networks, in
the second part of the thesis, we direct our attention from two-user cognitive networks to
the problem of smart interference management in large wireless networks. Here, we study
the problem of interference-aware wireless link scheduling. Link scheduling is the problem of
allocating a set of transmission requests into as small a set of time slots as possible such that
all transmissions satisfy some condition of feasibility. The feasibility criterion has traditionally
been lack of pair of links that interfere too much. This makes the problem amenable to
solution using graph theoretical tools. Inspired by the recent results that the simple approach
of treating interference as noise achieves maximal Generalized Degrees of Freedom (which is
a measure that roughly captures how many equivalent single-user channels are contained in
a given multi-user channel) and the generalization that it can attain rates within a constant
gap of the capacity for a large class of Gaussian interference networks, we study the problem
of scheduling links under a set Signal to Interference plus Noise Ratio (SINR) constraint.
We show that for nodes distributed in a metric space and obeying path loss channel model, a
re ned framework based on combining geometric and graph theoretic results can be devised
to analyze the problem of nding the feasible sets of transmissions for a given level of desired
SINR. We use this general framework to give a link scheduling algorithm that is provably
within a logarithmic factor of the best possible schedule. Numerical simulations con rm
that this approach outperforms other recently proposed SINR-based approaches. Finally, we
conclude by identifying open problems and possible directions for extending these results
Formulations and identification of algorithmic solutions for enabling opportunistic networks - M4.1
Milestone M4.1 del projecte Europeu OneFIT (ICT-2009-257385).This document contains a detailed description of the algorithms to be implemented to manage the opportunistic networks. There are defined according to the functional and system architecture (WP2) to fulfil the technical challenges.
These algorithms will implemented during the WP4.2 and validated during the WP4.3Postprint (published version
Advanced Trends in Wireless Communications
Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics
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